The invention relates to a compactor comprising at least one oscillating drum.
A generic compactor is known from EP 0 530 546 A. The known compactor comprises at least one traveling drum which is operatively connected with unbalance exciter shafts of an oscillation exciter, the shafts being arranged in parallel to the drum axis and rotating synchronously, such that the roller optionally applies a mainly dynamical shearing or pressure load to the ground.
A similar solution is known from DE 298 05 361 U.
The oscillation is generated by at least two exciter shafts with unbalance weights rotating in opposite directions. This results in a directed oscillation whose direction of action can be pivoted from a horizontal into a vertical direction. The amplitude of the roller drum remains constant such that only the direction of oscillation is changed.
Further, oscillation generation by means of circular vibrators is known. Here, the unbalance weights are preferably located on an axis in the center of the drum and generate a circulating force. If two unbalance weights rotating in the same direction are used, whose phases are adjustable relative to each other, the amount of the resultant compacting force can be changed by changing the phase position. Another parameter for adaptation to the operating conditions is the variation of the oscillation frequency.
A method for measuring mechanical data of a ground and for adjusting the roller parameters, based on the mentioned mechanical solution concerning adaptation of compacting force and frequency is known from WO 98/17865.
Proceeding from an oscillating drum with a circular vibrator whose amplitude and frequency are infinitely adjustable, the applicant dealt with automatic adaptation of the roller parameters traveling velocity, amplitude and frequency to the respective operating conditions. This type of amplitude and frequency adjustment is very complicated with regard to the configuration. The same applies to the adjustment of the direction of action of the oscillations in the aforementioned vibrators with unbalance weights rotating in opposite directions as described in EP 0 530 546 A and DE 29 805 361 U because here at least two exciter shafts are be used whose movements of rotation must be coordinated relative to each other.
Under comparable conditions, circular vibrators attain higher compaction values than the directed oscillation of vibrators with unbalance weights rotating in opposite directions. The directed oscillation of said vibrators generates pressure forces in the ground which act in one direction only and thus allow compaction by displacement of different layers of the subsoil to be compacted only to limited extent. If this direction of action of the oscillation is pivoted from a vertical into a horizontal direction, e.g. to reduce the oscillation transmitted to buildings, the shearing stress which can be transmitted to the subsoil becomes very small.
When applying the compaction method described in EP 0 053 598, compaction can optionally be carried out by using an oscillation effective in the depth according to the circular vibrator principle or using an oscillating drum movement generated by torques, said drum movement primarily producing shearing stresses in the subsoil. Like the adjustable vibrator with unbalance weights rotating in opposite directions, the oscillating drum movement reduces the oscillation stresses of the machine and the surroundings, but attains higher compaction values as compared with the vibrator with unbalance weights rotating in opposite directions. The method includes two exciter shafts synchronously rotating in the same direction of rotation and with a 180xc2x0 phase shift. Thus the oppositely directed forces generated by the exciter shafts and acting upon the drum are compensated. A torque about the drum axis acting upon the drum is generated. These torques with alternating signs lead to the oscillating movement of the drum, and a shearing stress with a comparably higher depth effect occurs in the subsoil. If a higher depth effect is required, the phase shift is reduced from 180xc2x0 to 0xc2x0 such that the effect of a circular vibrator is attained. An essential drawback of this concept is that the configuration does not allow infinite adjustment of the amplitude without the occurrence of undefined oscillation conditions. Another drawback is the high configurative expenditure.
It is an object of the invention to simplify a compactor of the aforementioned type with regard to its mechanical configuration, and to allow generation of an oscillation movement which optimizes introduction of a force into the material to be compacted to permit rapid compaction.
The invention advantageously provides that the oscillation exciter comprises a pendulum-type vibrator for generating elliptic oscillations of the drum, said vibrator having a pendulum-type housing oscillating about the drum axis and including a single unbalance exciter shaft supported in the pendulum-type housing at a radial distance to the drum axis and in parallel to the drum axis.
The use of a pendulum-type vibrator combines the advantages of the simple configuration of a circular vibrator and the adjustment capabilities of a directed vibrator with unbalance weights rotating in opposite directions as well as the advantages with regard to compaction of an oscillating drum movement. The unbalance weight rotating on the exciter shaft generates circulating forces. Since the exciter shaft is supported in a pendulum-type housing such that it is pivotable about the drum axis, only little forces are transmitted outside the direction of the longitudinal axis of the pendulum. The force components of the unbalance weights extending at an angle relative to the longitudinal axis of the pendulum generate a momentum about the drum axis acting upon the pendulum-type housing, and thus effect an excursion of the pendulum. Due to the high frequency of the unbalance weight and the mass inertia of the pendulum-type housing the angle of the pendulum movement can be kept small.
The pendular oscillations of the pendulum-type housing result in a generally elliptic form of oscillation of the drum.
The pendulum-type housing is preferably supported via rolling bearings on the inside of the drum radially on the drum. The radial support can be effected on the radially outer circumference portion of the pendulum-type housing or at corresponding radial housing steps of the pendulum-type housing at the axial side faces. The radial rolling bearings transmit the oscillations of the pendulum-type housing to the drum.
The angular position of the longitudinal axis of the pendulum-type vibrator relative to a vertical plane extending through the drum axis is adjustable with the aid of an adjusting means. Thus the orientation of the elliptic oscillation relative to a vertical plane extending through the drum axis is adjustable by e.g. xc2x190xc2x0. Between the adjusting means for adjusting the angular position of the pendulum-type vibrator and the pendulum-type housing a damping element allowing and limiting pendulum oscillations is arranged. The damping element serves as coupling element between an adjusting lever of the adjusting means and the oscillating pendulum-type housing. The adjusting lever presets the angular position of the longitudinal axis of the pendulum-type vibrator, wherein the damping element allows an oscillation of the pendulum-type housing about said angular position to a certain extent.
The longitudinal axis of the pendulum-type housing lies in a plane defined by the drive shaft of the pendulum-type vibrator and the unbalance shaft.
The elliptic form of oscillation generated by the oscillation drive is variable on the one hand via the angular position of the pendulum-type housing and on the other hand via the speed of the unbalance exciter shaft. Thus the direction of the elliptic oscillation and its intensity can be adjusted.
The drive shaft of the pendulum-type vibrator is arranged coaxially to the drum axis, wherein the drive shaft is supported in the pendulum-type housing.
The drive shaft for the pendulum-type vibrator is coupled via an intermediate gear with the unbalance exciter shaft. The intermediate gear may comprise a belt drive.
Alternatively, the unbalance exciter shaft can be adapted to be directly electrically or hydrostatically driven. In this case the intermediate gear and the drive shaft of the pendulum-type vibrator may be omitted, which reduces the configurative expenditure.
In one embodiment it is provided that, in axial direction, two drums are arranged side by side and comprise a common pendulum-type vibrator. The two drums may be provided with independent drum drives.